Method and apparatus for desurfacing metal



METHOD AND APPARATUS Fon nEsURFAcING METAL Filed Nov. 8'. 1940 INVENTORARTHUR P. SCHELLER ATTORNEY f//gw Patented July 2l, 1942 2,290,295 dME'rnoD AND APPARATUS Foa nEsUnrAc- ING tion .of Ohio METAL Arthur P.Scheuer, Irvington, N. J., The Linde .AirProducts Company,

assigner to a corpora- Application November 8, 1940, Serial No. 36l823.(Cl. 26S-23) 11 Claims.

This invention relates to a method of and apparatus for desurfacingmetal bodies, and more particularly to blowpipe nozzles, and the usingthereof, which are especially useful in connection with surface metalremoval'by effecting a progressive thermochemical reaction of such metalwith an oxidizing medium.

When an oxidizing gas stream o'f suitable character is directedobliquely against a work surface, such as that of a ferrous metal bodysuitably heated to an ignition temperature, and moved along saidsurface, a thermochernical reaction takes place between the oxygen andthe ferrous surface metal, which leaves a bright, clean area. Part ofthe metal removed is oxidized to form a molten slag and part of themetal is melted by the heat of the reaction. A wave of such mixed moltenmetal and slag is advancedioy the force of the oxidizing uid stream overthe surface metal to be removed and assists in properly heat- -ing thesurface portions of the base metal immediately prior to the actualdesurfacing reaction. In desurfacing a relatively wide area, it has beencustomary to arrange two or more blowpipe nozzles to direct oxidizingfluid jets against the work surface. Such nozzles had circular oxygenorices and produced substantially cylindrical oxygen jets flowing with arelatively low veloclty, i. e., a velocity below about 1000 feet persecond. Each such jet makes an individual groove in the work surface, sothat a ridge is formed between adjacent grooves by the desurfacingoperation.

Such ridge formation conceals and often contains defective metal whichit was intended to eliminate by the desurfacing operation. Also surfacedefects intended to be removed by the desurfacing, while removedcompletely within the channels, are only partially or removed not at allin the region of the ridges. Subsequent working or rolling of the metalbody causes the flaws or defects in the ridges to appear in the productand result in rejections, or they are further concealed, resulting inunsound steel or a product of poor quality.

In the desurfacing of blooms, billets, ingots and the like, it is thushighly desirable that the entire surface undergoing treatment beremoved, with the elimination of substantially all ridge formation, sothat the desurfaced area is substantially flat. l

Conventional desurfacing blowpipe nozzles have a relatively largecentral cylindrical oxidizture of fuel gas, such as acetylene, andcombustion supporting gas, such as air or oxygen. Thus, in operation, aseries of heating flame jets issue from such preheat gas passages. 'I'heoxidizing iiuid supplied to the central passage is preferably oxygen.The oxygen passage of such nozzles have generally been formed in amanner to cause expansion of the oxygen stream and a reduction of thevelocity of flow to a value below about 1000 feet per second or belowthe so-called acoustic velocity. The walls of such oxygen passages areeither cylindrical or constantly expanding from the inlet end toward theoutlet end of the nozzle and it has been found that, for satisfactorymetal removing eiiiciency, the range of variation in the rate of gas owthrough such nozzles is relatively limited. With' nozzles havingcylindrical orifices it has not been possible to remove surface metalefficiently so as to produce smooth channels with gas velocitiessubstantially exceeding the acoustic velocity. The use of a row of suchnozzles for desurfacing a wide area produces transversely concavegrooves divided by objectionable ridges, as pointed out above.

Therefore, the main objects of this invention are to provide: animproved method of and apparatus for removing surface metal from ferrousmetal bodies adapted to overcome the disadvantages and objectionablefeatures of the prior art in the matter of ridge formation; a method ofefficiently removing surface metal with oxygen streams flowing withvelocities exceeding the acoustic velocity; and apparatus for carryingout such method for removing a wide layer of surface metal to asubstantially constant depth to produce a new surface substantially freefrom. ridges.

The above and other objects and novel features of this invention will'become apparent from the following description taken with theaccompanying drawing in which:

Fig. 1 is a fragmentary perspective view of a desurfacing unit embodyingthe principles of this invention in operation; I

Fig. 2 is a view in front end elevation on an enlarged scale of ablowpipe nozzle constructed f* according to the invention;

Fig. 4 is asimilar view in longitudinal section -of a,modiiled form ofnozzle according to the ing fluid outlet passage surrounded by a concenltric series of equally spaced preheat gas passages. The latter aresupplied with a. combustible mixinvention;

Fig. 5 is a fragmentary perspective view showing the location of theinserts in the nozzle the end portion of the nozzle being indicated bybrokenlines.

Fig. 6 is a fragmentary view of a longitudinal section taken on the line6-6 of Fig. 3 showing an insert and the lateral slots.

In general the improved blowpipe nozzle according to the invention isparticularly adapted for a multiple nozzle desurfacing head or unit asillustrated in Fig. l. Each nozzle has the outlet portion of itsdesurfacing oxygen passage shaped so that it changes smoothly from acircular passage to a slot-like exit orifice having substantially flattop and bottom edges and the passages are so shaped as to produce auniform velocity distribution. Such nozzles make individual grooves thatare substantially ilat, and when suitably spaced in a row in` adesurfacing head, the edges of the adjacent oxygen streams merge toproduce a substantially continuous wide desurfacing-stream thereby toeliminate or greatly reduce the objectionable ridges and remove all thedefective surface metal.

coincides with the discharge end face II, and the oblique planes ofwhich are equally inclined relatively to the ax-is of the bore I3 andintersect along a line which intersects said axis perpendicularly at anexternal point in front of the face II. The inserts I 6 taper inwardlytopoints I1 on elements of the bore I3 spaced at 90 from the elements ofthe bore on which are located The cross-sectional -area ofthe slot-likeexit orifice, for best results, may be the same as, or slightly lessthan, the cross-sectional area of the circular passage adjacent to thealtered portion. The cross-sectional area of the altered portion iseither constant oruniformly reduced, so that the passage is streamlinedand has no abrupt changes in its cross-sectional area.

According to this invention, the nozzle N may be produced from a. blankof a conventional blowpipe nozzle having an axial oxygen passage 0 byforming a concentric series of suitably spaced longitudinal preheatpassages?, in the nozzle blank and modifying the orifice end portion ofthe passage O. Diametrically opposed divergent slots or grooves I0, IIIare then machined in the body of the nozzle in the walls of the oxygenpassage O. The slots I 0 are of greatest depth at the end face I I ofthe nozzle andvextend inwardly to a point I2 where their depth taperstozero. The walls of the slots III are preferably in the shape ofsections of oblique cylinders the bases of which lie in the plane of theface II and theaxes of which are inclined at equal angles relatively tothe axis of the passage O and intersect at a point on said axis withinthe nozzle.

The nozzle blank employed for the form of nozzle illustrated in Figs. 2,3, 5, and 6 has an oxygen passage O comprising cylindrical bore changedsmoothly from a cylindrical flow to a portion I3 extending back from theface Il, a.

constricted inlet portion Il and a tapered portion I5 joining the inletIl and the bore Il. The inlet Il is of a diameter to pass the desiredvolume of oxygen' when the oxygen is supplied at a suitable headpressure through a supply passage S in a blowpipe head indicated at H.The blowpipe head H is preferably of a type suitable for receiving aclosely spaced row of desurfacirlti` blowpipes and has nozzle receivingopeningsof the customary construction adapted to receive and hold thenozzles N, the nozzles N being retained by ring nuts R acting against ashoulder K adjacent the inlet end` of the nozzles.. The preheating gaspassages P of the nozzles are supplied with mixed combustible gas by achannel C in the head H with which they communicate.

To form, with the slots III, the delivery orifice of the nozzleaccording to the invention, a pair of tapered inserts I6, I6 are thensecured within the bore I3 adjacent the face II opposite each other. Theinserts Ilpreferably comprise oblique sections of a right cylinder thecylindrical surface portion of which coincides with and is in contactwith the bore I3, the base of which insert h points I2.

The inserts I6, I6 are disposed so that their straight base edges arealined with the slots III;

In the form ofenozzle illustrated in Fig. 3 the I oxygen flow is meteredby the inlet restriction I4. The stream`of oxygen then expands in theportion I5 at a rate suflicient to effect a. reduction of velocity. Inthe portion I3 the stream becomes substantially non-turbulent and in theportion of the passage between the faces of the inserts I6 and beyondthe points I1, the flow is sectionally oval flow, the stream "becomingribbon-like at the exit facel I I, that is, like a ribbon of substantialthickness having non-parallel edges since the stream continues to expandin width at a substantial rate as well as slightly in thickness afterleaving the nozzle. In the portion of thelpassage from points I1 topoints I2 the cross-sectional area gradually decreases and the flowvelocity increases. the end face I I, the upper and lower walls of thepassage continue to converge but the side walls of the passage which arenow formed by the slots I0, diverge. 'I'he rate of such divergence is sochosen that the cross-sectional arca of the passage in the plane of theface II is substantially equal to the cross-sectional area of thepassage in the region of the points I2. With such relation betweenv theupper and lower' and side walls of the passage, it is found that theribbon-like stream of oxygen produced by the nozzle flows with asubstantially uniform velocity throughout the entire width of thestream. It is important that the velocity be uniform in order to producesubstantially flat desurfacing cuts. Furthermore the stream expands verylittle'in the vertical direction but will expand edgewise or laterallyjust the right amount to merge properly with adjacent streams whenseveral such nozzles Fig. 1.

In the modified form of no zzle illustrated in Fig. 4 and which has anend. view appearance similar to Fig. 2, the cylindrical bore llis oisubstantially constant diameter to the inlet end of the nozzle N' andthe slots I0' taper to points I2' which are substantially in the sametransverse right plane as the points I1 of the inserts I6. The oxygenpassage in this form of nozzle is substantially of constantcross-sectional area throughout. The control of the quantity of oxygenflowing may be eiected by a metering passage in the blowpipe head or bycontrolling the flow rate to the nozzle. The diversion of the side wallsof the passage from the points I2' to the face II is preferably such asto balance the convergence of the top and bottom walls from the pointsI1 to the face II so that the crosssectional area of the passage in theplane of From the points I2 to l as the area of the slotted end orifice.If desired, the nozzle N may also be provided with an inlet restrictionsimilar to passage I4.

The resulting arrangement is preferably such that there is provided astreamlined oxidizing fluid flow passage at least the end portion ofwhich is of substantially constant cross-sectional area and has across-sectional shape that gradually changes from circular to oblongshape at the discharge face II of the nozzle. The long sides of theoblong shape are straight and substantially parallel, and the shortsides thereof are preferably curved.

The above-described method of making the nozzles is simple andrelatively inexpensive because the parts are readily available and thereresults a precision instrument. However, various changes may be made inthe detailed method of construction disclosed therein without departingfrom the principles of the invention provided that substantially thesame shape of oxygen passage results. For example, the nozzle maybeformed from a single piece of metal.

'Ihe blowpipe nozzles N or N are assembled in a desurfacing apparatusindicated fragmentarily at A and comprising a head plate I9 throughwhich the individual nozzles pass and are supported in' a row forlongitudinal and rotational adjustment. The nozzles are preferablypositioned with the long sides of the orifices in parallel relation tothe surface 20 of the work W which may be the top surfaceof a steelbillet,-

ingot or slab. The axes of the nozzles are held at an acute angle to thesurface 2l) in order to impinge the oxidizing streams 2l along andobliquely against the surface. The slot-like exit orifices of thepassages O and O' are arranged in transverse alinement for normaloperation and the nozzles are spaced so that the oxygen streams 2|combine or merge smoothly into one Wide substantially continuous fiatsheet at the zone of reaction indicated at Z, thus, advancing the moltenmetal and slag in a uniform wave 22 and leaving a clean, fiat, newsurface 23 cn the work.

The desurfacing apparatus A may be normally stationary while the work Wis moved relatively thereto toward the plate I 9, but, if desired, theWork may be stationary while the apparatus A is advanced for thedesurfacing operation. The lower surface of the plate I9 preferably isguided on the surface 23 to maintain the nozzle orifices at a constantelevation from the work surface. The preheating flame jets issuing fromthe preheat passages P operate inthe usual way to assist in maintainingthe thermochemical reaction of the oxygen with the ferrous surface metalundergoing treatment.

In some cases the surface defects may be deeper and more concentratedalong certain portions of a surface, such as along the edges of billets.When it is desirable to remove a greater depth of metal along certainportions of the surface, one or more of the nozzles is fractionallyturned about its axis so that the lower edge of its orifice is notparallel with the work surface. Each such nozzle with a non-parallelorifice will produce a substantially fiat bottcmed groove the depth ofwhich varies transversely f the groove. The nozzles also may bestaggered in their distances from the work surface, as desired.

The use of blowpipe nozzles of this invention in a multiple nozzledesurfacing head results in the removal of a uniform layer of metal fromthe Work surface, leaving a surface that is free of ridge formation.Thus, all surface defects and fiaws which are no deeper than the depthof the desurfacing operation are removed. The desurfaced area may be ofuniform or uniformly varied depth, as desired, and more of the defectivesurface metal is removed than is possible with conventional nozzles.

With conventional round nozzles it is usually necessary to remove metalto a greater depth at the center of the channels produced than the depthof the defects in order to remove most of the defective surface metal.When a uniform layer of metal is removed the depth of removal need notbe as great in order to remove all defects and therefore the employmentof nozzles according to this invention will provide greater over-alleconomy.

Good results have been' obtained with a nozzle embodying the principlesof this invention `and having an oxygen passage provided with an inletrestriction of about .277 inch diameter, a maximum cross-sectional areaof about .135 square inch and aV cross-sectional area at the end orificeof about 0.067 square inch, the width of the slot being about 1/8 inch.Such a nozzle will produce an oxygen stream effecting eiiicient surfacemetal removal with a relatively wide range of gas ow rates between about1500 cubic feet per hour to 3500 cubic feet per hour and streamvelocities of from about 600 feet per second to about 2000 feet persecond or considerably in excess of the acoustic .velocity. Thesevelocities are on the basis of normal temperature and pressureconditions as the conditions in the stream are diicult to measure.

It will be noted that the narrow sides of the oxygen passage ofthe'nozzle of this invention diverge or fiare outwardly. The angle ofdi` vergence preferably should be such that the oxygen streams wherethey strike the work surface merge' to form a sheet of oxygen ofsubstantially uniform depth transversely ofthe surface. If there is-toomuch overlapping of the oxygen streams there will be a gouging effect sothat instead of removing undesirable ridges, grooves may be producedwhich are also undesirable.

With the specific example of nozzle disclosed above and having theorifice side walls diverging to include an angle of about 24, thecenter-tocenter spacing of the nozzle orifices in the head A should beabout l; inches. It has been found that substantially fiat surfaces areproduced when thespacing is between 111g inches to about 11A inches. Ithas also been found that a divergence of the side walls of the outletpassage in conjunction with a convergence of the top and bottom walls isessential to produce a uniform distribution of velocity of flow of thestream throughout the width of the ribbon-like stream. If the divergenceis too small or too great, the velocity distribution becomes uneven anda nonuniform depth of cut will result.

` The oxygen streams from the desurfacing nozzles are directeddownwardly and obliquely onto the work surface in the general directionof advance and the reaction puddle formed by each jet or stream lisproportional to the size and shape of the cross-sectional area. of thesurface metal removed by the desurfacing operation. The length of theindividual puddles or of the combined puddle, measured in the directionof advance, must be appreciable, to maintain the stability of thedesurfacing operation. 'Ihat is to say, if the puddle or wave of moltenmetal and slag is too short the desurfacing operation may be -lost or'bedeflected by irregularities of the 'original surface. 'Ihe length ofpuddle is dependent on the thickness of the stream..and therefore theoxygen stream must be of suiiicient thickness to maintain a puddle oi'sumcient length. The' vertical or shortest dimension of the .oxygenstream also must not be too narrow or the` stream will tend to deformand become feathery. 'I'his is probably due to the friction effects ofthe sidewalls of the orifice and turbulence caused by the surroundingair. l

It has alsorbeen discovered that for the purpose of making asubstantiallyflat cut, it is essential that the bottom surface of thestream .shall be fiat. v'1'herefore,` the lower edge of the surfaceremoval with smaller loss of surfacei metal, stability of operation, andexcellent economy.

Other uses for the nozzle disclosed herein may be found and it will beapparent that modifications of the nozzle may be made and in the processof making and using the nozzle and that certain features can be usedindependently of others without departing from the spirit and scope ofthe invention as set forth in the claims. For example, the upper insertmight be omitted altogether or there may be substituted for the upperinsert I6 an insert which does not have a fiat oblique surface but onethat is higher in` its center portions. Where oxygen is named in theclaims it should be understood to include not only substantially pureoxygen but also oxygen containing mixtures.

I claim:

1. A method of thermochemically removing surfacev metal from ferrousmetal bodies which comprises heating at least a portion of the metal tobe removed to an ignition temperature; forming a ribbon-like oxygenstream to flow with a velocity of flow substantially exceeding theacoustic Yvelocity and with substantially uniform velocity throughoutits width, said stream having a relatively flat bottom surface anddiverging lateral sides; directing said stream obliquely against andalong .said heated portion of surface metal and with said.bottom surfaceadjacent said surface of the body; and relatively moving said stream andsaid body to advance said stream along said surface in the direction ofsurface metal to ybe removed.

2.- In a method of. thermochemically removing surface metal fr m ferrousmetal bodies by applying obliquely ainst and along a surface of saidbody heated v the ignition temperature, a stream of oxygenv andrelatively moving such stream and said body, the steps comprisingincreasing the velocity of flow of said stream to values substantiallyexceeding the acoustic velocity. and so forming said stream that asubstantially uniform layer of surface metal is removed by effecting agradual conversion of the form of the streamfrom substantially round incross section to a laterally wide form having divergent lateral edgesand a substantially at lower side adjacent the surface of said body.

3. A method of thermochemically removing surface metal from ferrousmetal bodies which v comprises heating at least a portion of the metalto be removed to an ignition temperature; forming a row of ribbon-likeoxygen streams,- each to flow with substantially uniform velocitythroughout its width, said streams having nat lower sides substantiallyin alinement and latl eral diverging sides; spacing said streams so thatadjacent diverging sides thereof merge suiliciently to form in effect asubstantially uniform wide desurfacing stream; directing said streamsobliquely against and along said heated portion of surface metal andwith said flat sides adjacent the surface of said body," and relativelymoving said desurfacing stream and said body to .advance said streamalong said surface in the direction of surface metal to be removed.

4. A method of thermochemically removing surface metal from ferrousmetal bodies according to claim 3 in which the velocities of flow ofsaid streams are .increased to values substantially exceeding theacoustic velocity.

5. A method of thermochemically removing surface metal-from ferrousmetal bodies according to claim 3 including the step of so spacing saidstreams with respect to the angle of divergence of said sides that thesurface removing action of ysaid row of streams is substantially uniformacross the entire width of surface impinged, whereby the surface metalis removed to a constant depth..

6. A method, of thermochemically removing surface metal from ferrousmetal bodies which comprises heating at least a pou-tion of the metal tobe removed to an ignition temperature; providing a stream of oxygen ofsuitable volume and pressure; effecting a reduction of the velocity offlow of said stream by expansion; re-

ducing the. turbulence of said stream; increasing the flow velocity ofsaid stream by gradually decreasing its cross-sectional area; thenconverting said stream to a substantially ribbonlike form having anincreased ilow velocity by effecting a simultaneous reduction of thethickness andan increase of the width of the stream without substantialchange of its cross-sectional area; and directing such ribbon-likeoxygen stream obliquely against and Aprogressively along said h'eatedportion of surface metal whilev a wide side of said stream is maintainedadjacent said surface, to remove a layer 'of surface metal having asubstantially flat contour.

7. A method o f thermochemically removing surface metal from ferrousmetal bodies which comprises heating at least a portion of th'e metal tobe removed to an ignition temperature; providing a-relatively voluminousstream of oxygen to flow at a relatively low velocity; reducing theturbulence of said streams; increasing the flow velocity of said streamby gradually but slightly decreasing the cross-sectional area of saidstream: then converting said stream to a substantially ribbon-like formhaving an inface metal while a wide side of said stream is maintainedadjacent said surface, to remove a layer of surface metal having atransversely fiat contour.

8. Desurfacing apparatus comprising a plurality of blowpipe nozzlesarranged in a row to impinge oxidizing fluid streams along and obliquelyagainst a ferrous metal body for thermochemical reaction with heatedsurface metal, said nozzles each having smooth oxidizingl fluid flowpassages including an intermediate portion, a slot-like exit oriiice,upper and lower wall portions that smoothly converge from saidintermediate portion toward said exit orifice, and side wall portionsthat diverge from the width of said intermediate portion to the width ofsaid orifice, the cross-sectional area of the passage where said sidedivergence begins being substantially equal to the cross-sectional areaof said exit orice and the exit orifices of said nozzles being alined toproduce a sheet-like oxidizng gas stream of substantially eventhickness, and means associated with said oxidizing gas 'exit orificesfor heating at least a portion of said surface metal to the ignitiontemperature.

9. Desurfacing apparatus as defined by claim 8 in which thecenter-to-center spacing of said nozzles are correlated withthedivergence of said side walls to insure the removal of surface metalto a substantially constant depth.

10. Desurfacing apparatusV as defined by claim 8 including meanssupporting each of said blowpipe nozzles lfor rotational adjustment.

l1. Desurfacing apparatus as defined by claim 8 in which the divergenceof said side wall portions of said oxidizing gas passage is such as toinclude an angle of about 24 degress and the center-to-center spacing ofsaid nozzles is between l; inches to 11A inches.

ARTHUR P. SCHELLER.

